Hydrogenation consists of the addition of hydrogen to the double bonds of fatty acids, increasing the saturation of the fatty acids. In the hydrogenation of triglycerides, the reaction typically takes place by contacting triglyceride with gaseous hydrogen at a temperature above about 302.degree. F. (150.degree. C.), in the presence of a solid catalyst. It is known that increasing the pressure increases the rate of the triglyceride hydrogenation reaction. Swern, Bailey's Industrial Oil and Fat Products, Vol. 2, 4th ed., Interscience Publishers, NY, pp. 5-69 (1982), discusses the hydrogenation process in general.
Fatty acid esters of sucrose ("sucrose polyesters") are usually synthesized by one of three methods: transesterification of the sucrose with methyl, ethyl or glycerol fatty acid esters; acylation with a fatty acid chloride; or acylation with a fatty acid per se. As an example, the preparation of sucrose fatty acid polyesters is described in U.S. Pat. Nos. 2,831,854 and 3,521,827 (herein incorporated by reference).
More highly saturated sucrose polyesters are generally made by using more saturated fatty acids as the starting material prior to esterification. The present invention, on the other hand, concerns a method for increasing the saturation of sucrose polyesters by hydrogenating the polyesters after they have been synthesized from sucrose and fatty acids, i.e., "post-hydrogenation".
It is, therefore, an object of the present invention to provide an effective process for the post-hydrogenation of sucrose polyesters.
It is another object of the present invention to use the post-hydrogenation process to make sucrose polyesters that are different from those made by esterification alone.
It is a further object of the present invention to provide a post-hydrogenation process that allows more complete hydrogenation of certain kinds of sucrose polyester molecules.
These and other objects of the invention will be made clear by the disclosure herein.
All percentages are by weight unless otherwise defined.